Thank you for your question regarding the measurement of earth resistances for telecommunications sites. The test you are referring to is for measuring the resistance-to-ground of the telecommunication sites grounding system. This determines the effectiveness of the grounding system in the soil located at the site. You are correct in being concerned about the nearby tower. Objects that are connected to the ground grid, especially when dealing with 3-point test method, can cause erroneous measurement results. Even when an object is not directly connected to the grid, but only near it, can result in measurements that are negatively impacted. And often, soil resistivity testing is needed in addition to the resistance-to-ground test to accurately determine the final earth resistance of a grounding system.
There are two accepted test methods for this test: the 3-point Fall-of-Potential Test Method, and the Induced Frequency Clamp-On Test Method. Both tests require a signal to be injected into the grounding electrode system with a return source that forces the signal to propagate through the earth (soil). The primary difference between the two test methods is the signal return source. The 3-point test uses a probe placed into the earth at a specified distance relative to the size of the grid, the Clamp-On test uses the utility company’s ground grid as the reference (return source). More information can be found here:
Whichever test you choose to measure the earth resistance of your site, it is important to note that both tests can easily be done incorrectly. The most common problem with the measurement of ground grid resistance’s to earth, is poorly trained operators. Also, it is quite possible that the way your grounding system was physically wired will prevent either test from being used at your site. In that case, only computer modeling is available for calculating the earth resistance of your grounding system.
We are of course more than happy to help with your testing needs, but if not us, please seek assistance from someone who has the proper equipment and knows how to properly conduct these tests. We hope you find this information useful. Feel free to call us and one of our engineers will be glad to discuss your project with you free of charge.
The Engineering Team at E&S Grounding Solutions
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